| Manufacturer: | Fluke |
| Model: | 8100B |
| Year: | 1973 (1969) |
| Schematic: | MF |
| |
| Functions: | DCV, ACV, Ohms |
| Display: | NIXIE |
| Digits: | 4 |
| Logic: | DTL,TTL |
|
This model is based on another novel A-D conversion technique called
"Recirculating-Remainder A-D Conversion" by Fluke.
The technique can be described as performing long division with analog values.
A counter, resistive D-A ladder and comparator are arranged in a typical staircase A-D loop
but this arrangement is only 4 bits wide: only enough for one decade of resolution.
The process starts by using this single-digit A-D converter to resolve the most significant
digit.
The analog difference between the input value and the D-A ladder (the remainder)
is stored in a sample-and-hold circuit, multiplied by 10 through an op amp,
and fed to the single-digit A-D converter to resolve the second digit.
The process is then repeated to resolve the 3rd and 4th digits.
This results in a minimal component count on the digital side with
only 3 digital ICs: a 4-bit counter, a NIXIE decoder/driver and a triple NAND gate.
On the analog side numerous JFETs are used as analog switches.
This model has auto-polarity but not auto-ranging.
- Unit Log -
| Serial Number: | 58412 |
| Year of Manufacture: | 1973 (transistor date code of 7301). |
| Date of Receipt: | 11 May 2008 |
| State upon Receipt: | Good physical condition but not functional.
Display stuck at 2222 on all functions. |
| Date: | 14 May 2008 |
| Symptoms: | Display stuck at all 2s. |
| Analysis: | All 3 digital ICs found to be faulty. |
| Solution: | Replaced.
839 DTL 4-bit counter replaced with 74LS197.
Display now varies in accordance with applied voltage, but is way off linear,
making large jumps along the way. |
| Date: | 14 May 2008 |
| Procedure: | Trim pots marked to indicate original positions,
then turned to clear any bad contact problems. |
| Date: | 18 May 2008 |
| Symptoms: | Continuing from 14 May. |
| Analysis: | Stepping function during count as seen at TP2 doesn't seem quite right.
Surmise that there is a problem around the primary DA ladder.
Output from Q43,Q44 not changing.
BE junction of Q45 is open. |
| Solution: | Q45 replaced.
Unit is now functional in DCV and KOhm modes, and fairly accurate even with no recalibration.
ACV mode still has a problem. |
| Date: | 18 May 2008 |
| Procedure: | Cleaned. |
| Date: | 24 May 2008 |
| Symptoms: | ACV mode does not work properly (cont'd from 18 May 2008). |
| Analysis: | TP9 shows a negative voltage during input sample phase (¯1) with in-range AC input,
whereas it should be positive.
Suspect a problem with Q16 as the only negative voltage nearby is the gate of Q16
during other phases. |
| Solution: | Q18 moved to Q16. 2N5459 inserted for Q18. (Vdss of 2N5459 is 25V rather than preferred 30V.)
Unit reassembled. Fully functional. |
